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An anti-Brexit supporter holding a European flag protests outside the Houses of Parliament in London on Nov. 15, 2018.

Matt Dunham/The Associated Press

Now that the U.K. and the European Union have reached a draft withdrawal agreement, both sides begin the long and arduous process of getting it approved. Prime Minister Theresa May began making her case Thursday in the British House of Commons but five cabinet ministers have already quit, including Brexit secretary Dominic Raab, who resigned Thursday morning, and there could be more to come. Here’s a look at what happens next and the many pitfalls that could occur.

First there will be a special summit of EU leaders, likely on Nov. 25, where the deal will be reviewed. It’s expected to be approved easily, although officials in France, Germany and the Netherlands have said they want to take a close look to make sure the U.K. isn’t getting any special advantages.

The next big hurdle comes in early December when the British House of Commons will vote on the agreement. Prime Minister Theresa May’s Conservatives don’t hold a majority of seats and up to 50 Tory MPs have said they won’t vote for the deal. Northern Ireland’s Democratic Unionist Party, which has been propping up Ms. May’s minority government, has also said it doesn’t like the deal. And the leaders of all the opposition parties, including Labour, have come out against it. All of which means Ms. May will have to do a lot of arm twisting and convincing to find enough support to get the agreement approved. That’s not impossible, as some Labour MPs could defy their leader and back the agreement, but it won’t be easy. If the agreement is voted down, the government has 21 days to come back with something different. If that also fails, no one knows what will happen. The U.K. could leave the EU in March without a deal, there could be an election, or the government could hold a referendum on the proposed agreement.

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The European parliament and all EU member states also have to approve the withdrawal agreement. There’s less likelihood of opposition here, but surprises can happen. Remember when Wallonia held up the Canada-EU trade deal?

And one other thing to keep in mind: This is only the withdrawal agreement. Both sides haven’t even started negotiations on a trade deal. And that could take years.

Here are some more key dates and figures: